This invention relates generally to roll-compensating apparatus and methods and more particularly, but not by way of limitation, to apparatus and methods for compensating for the angular movement of a scanner platform about an axis which is the axis about which a scanner device mounted on the scanner platform rotates.
To obtain information from an object, there are data acquisition apparatus and methods for scanning the object. Such apparatus and methods are responsive to optical, infrared, or other suitable inputs emitted or reflected by the object as is wellknown in the art.
One such scanning apparatus functions by moving in a direction relative to the object and concurrently conducting a series of scans which cover discrete paths along the object extending transversely to the direction along which the scanner apparatus moves relative to the object. This series of scans is accomplished with a scanner device mounted on a support member so that the scanner device can rotate through a predetermined angle to scan that portion of the object which falls within the predetermined angle.
It will be appreciated that if the support member rolls or has angular movement relative to the axis of rotation of the scanning device, the end limits of the scans defined by the predetermined angle will be offset so that the ends of one scanned path will not be properly aligned with the ends of each of the other scanned paths. When such rolling occurs, the information received by the scanner device will be distorted in that the scanner device will perceive the detected information to be related to the other information received by the scanner device in a manner which is different from the actual relationship between the different items of information. Therefore, there is the need for an apparatus and method by which the scanner device can be maintained in proper relationship with the scanned object despite any roll of the support member about an axis which is the same as or parallel to the axis of rotation of the scanner device.
Various types of scanning apparatus and methods are known to the art. In U.S. Pat. No. 3,039,002 to Guerth there is disclosed an electro-optical tracking apparatus which utilizes a center line scan of one field scan to correlate with a second field scan by finding the corresponding center line of the second field scan.
In U.S. Pat. No. 3,634,008 to Plummer there is disclosed a device for panning a camera to keep the camera constantly aimed upon a stationary subject irrespective of the camera displacement.
In U.S. Pat. No. 3,278,746 to Fiat there is disclosed the concept of a mechanism which provides an electrical output signal indicative of the roll of an aircraft about a longitudinal axis. This output is utilized to dynamically position a mirror to compensate for or eliminate the effects of roll of the aircraft.
I am also aware that in the LANDSAT satellites there is a scanning apparatus which reciprocates in a raster-like manner and which obtains data during scans conducted in one direction of the reciprocating movement.
Despite the aforementioned disclosures, there is the need for a simplified roll-compensating scanning apparatus and method for maintaining the proper relationship between a scanner device mounted on a platform which is susceptible to roll and an object from which the scanner device is to receive information.